You are correct, mister Maokai. It all depends on the map type Destroyer is going for.
In a moba, you want ultimates that will give your team of X heroes the upper hand in a hero vs hero battle, may it be high single target damage, high crowd control, or utility.
In melees (as in warcraft III melees), most of the time, you're aiming at stuff that will give your *army* of a couple dozens of units the upper hand, mostly through utility. Just take a look at W3 ultimates :
Priestess of the Moon's ultimate, if channeled for its full duration, deals enough damage to single-handedly tear down the whole of the enemy's forces, usualy through ridiculous utility (Reincarnation, Big Bad Voodoo, Tranquility, Animate Dead), huge splash damage (Volcano, Moonfall, Death and Decay, Locust) or through extremely powerful summons (Inferno, Phoenix, Vengeance, which are all wayyy more powerful than Tibbers from LoL).
Generally speaking, ults from melee-W3 are much more powerful than LoL ults, or even (sometimes) DotA ults (which are themselves ridiculously powerful to compensate for the lack of AD- and AP-ratios), but are very rarely used for the same thing.
Which is all why I think your spell idea would make a great basic spell, but an ultimate, not so much
... Also I didn't make such a constructive response just to prove a point, hopefully this gives you ideas for the future of your map, Destro.
... I might make a tutorial for good ultis.
